Nonwoven fabrics are used in a wide variety of applications where the engineered qualities of the fabric can be advantageously employed. These types of fabrics differ from traditional woven or knitted fabrics in that the fibers or filaments of the fabric are integrated into a coherent web without traditional textile processes. Entanglement of the fibrous elements of the fabric provides the fabric with the desired integrity, with the selected entanglement process permitting fabrics to be patterned to achieve desired aesthetics.
Various prior art patents disclose techniques for manufacturing nonwoven fabrics by hydroentangling processes. U.S. Pat. No. 3,485,706, to Evans, hereby incorporated by reference, discloses a hydroentanglement process for manufacture of nonwoven fabrics. Hydroentanglement entails the application of high-pressure water jets to webs of fibers or filaments, whereby the fibers or filaments are rearranged under the influence of water impingement. The web is typically positioned on a foraminous forming surface as it is subjected to impingement by the water jets, whereby the fibers or filaments of the web become entangled, thus creating a fabric with coherency and integrity, while the specific features of the forming surface act to create the desired pattern in the nonwoven fabric. However, there is no teaching or suggestion in Evans '706 to form a fabric upon a three-dimensional forming surface.
Heretofore, typical hydroentanglement of relatively low basis weight fabrics with the Evans-type technology has been problematic. At low basis weights (on the order of less than 30 grams per square meter), there are a relatively low number of fibers or filaments present for entangling, thus making entanglement relatively inefficient. Entanglement of these light basis weight webs on traditional forming surfaces taught by Evans and its progeny tends to "wash" the low fiber content webs, rearranging the fibers in a fashion which undesirably results in a non-uniform product. Entanglement of these low basis weight webs at relatively high processing speeds compounds the problem of maintaining uniformity, because the impinging water jet flows and/or pressures must be relatively increased, which increases the undesirable tendency to distort the web. Further, the high energy jets required by high speed entangling processes tend to drive the fibers into the drain hole openings of the foraminous surface, or into the interstitial spaces of a woven forming wire. This creates serious difficulties with web transfer.
U.S. Pat. No. 5,369,858, to Gilmore et al., discloses a process for forming apertured nonwoven fabric from melt-blown microfibers using the Evans-type technology. These types of fibers are attenuated during known melt-blowing formation techniques, whereby the fibers have relatively small diameters. This patent discloses the use of a belt or drum forming surface having a perforated or foraminated forming surface. Plural hydroentangling manifolds act against fibers positioned on the forming surface to displace the fibers from "knuckles" of the forming surface, and into openings or lower parts of the forming surface topography, as in Evans. This patent contemplates use of a polymeric net or scrim for fabric formation, and the formation of fabric having apertures therein of two different sizes, including formation of fabric from a first layer of textile fibers or polymeric filaments, and a second layer of melt-blown microfibers.
U.S. Pat. No. 5,516,572, to Roe, discloses a disposable absorbent article including a liquid pervious topsheet, wherein the topsheet comprises a nonwoven fabric prepared from a homogeneous admixture of melt-blown fibers and staple length synthetic fibers. The patent contemplates that fabrics formed in accordance with its teachings comprise a blend including up to 50% by weight of melt-blown fibers.
U.S. Pat. No. 4,805,275, to Suzuki et al., also discloses a method for forming nonwoven fabrics by hydroentanglement. This patent contemplates that hydroentanglement of a fibrous web be effected on a non-three-dimensional smooth-surfaced water-impermeable endless belt, but notes that at fabric weights below 15 grams per square meter that irregularities in the fibrous web occur, and fabrics with substantial uniformity cannot be obtained.
In contrast to the above-referenced patents, the present invention contemplates a process employing a hydroentangling device having a foraminous forming surface for forming relatively low basis weight nonwoven fabrics, which can be efficiently practiced for manufacture of fabrics having a high degree of uniformity. Such uniformity facilitates use of such fabrics in a wide variety of applications, with efficient formation facilitating economical use.